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MIThril 2003 Architecture OverviewThe MIThril 2003 hardware architecture is a highly flexible, modular system that is tied together by wired/wireless networking protocols and a unified multi-protocol wired power/data bus, called the MIThril Body Bus, for sensors and peripherals. While variety of hardware configurations are supported by the MIThril 2003 architecture, the wearable systems that are in predominant use is a PDA-based system with sensor hub and distributed sensor network.
Figure 2: MIThril 2003 system, comprised of the Zaurus PDA (right) with SAK2 sensor hub and
physiological sensing board (top), EKG/EMG/GSR/ temperature electrodes and sensors (left) and
combined three-axis accelerometer, IR tag reader, and
RS232/I2C bridge (bottom)
MIThril 2003 Computing NodesFor applications requiring real-time data analysis, peer-to-peer wireless networking, full-duplex audio, or graphical interaction, MIThril employs Linux-based single-board computers or PDAs, The PDA-based MIThril 2003 system shown in the figure above uses the Sharp Zaurus SL-5500 PDA. We chose the Zaurus SL-5500 as the basis for this configuration because it provides excellent Linux support combined with a range of capabilities in an inexpensive, commercially available package.
The Zaurus SL-5500 is a complete embedded Linux system that is capable of doing substantial on-board processing. It provides all of the elements of a stand-alone computer system, including a 206-Mhz StrongARM processor, 64 MB SDRAM, 16 MB ROM, CF and SD expansion slots, full duplex audio, qVGA color touch screen, and an integrated QWERTY keyboard.
The Zaurus SL-5500 provides a significant amount of on-board processing power, vital for being able to do real-time sensor processing. As a reference point, the 206-Mhz StrongARM processor has approximately 3x the performance of a desktop Pentium-166 . Wireless network connectivity is obtained through an WiFi-enabled CF card, and ample storage is provided via the SD slot (up to 1 GB).
The CF card slot enables a rich variety of peripherals to be attached, including cell-phone modems, image and video cameras, Bluetooth and 802.11b (WiFi) wireless, and even head mounted displays – The MicroOptical VGA color HMD is now available from Interactive Imaging Systems  with a CF interface that works under Windows Pocket PC. We are now working on a Linux driver for this device.
The Zaurus also provides an RS232 serial port, which we use to interface with the MIThril sensor hub described below.
MIThril 2003 Sensor Hubs
The SAK2 sensor hub is used to interface the Zaurus SL-5500 with the MIThril body bus. This hub bridges between the RS232 serial interface on the Zaurus and the Phillips I2C multi-device serial protocol used on the MIThril body bus.
When connected to the Zaurus, the sensor hub is responsible for sensor data acquisition, buffering, and sequencing. We use the SAK2 board as the sensor hub, which also provides stand-alone data acquisition capabilities in the form of a CF storage card interface, a real-time clock for sequencing, battery power, and an optional 2.4 Ghz wireless transceiver. The SAK2 supports sensor daughter boards as well as I2C devices through its MIThril body bus.
Because the sensor hub is a generalized data acquisition board, it can be used in stand-alone mode as a dedicated wearable for a variety of applications. A small sample of applications includes social network experiments, real-time critical health monitoring, and identifying activities of daily living.
MIThril 2003 Sensor Hardware
Although we have developed prototype USB sensors, virtually all MIThril 2003 sensors are either stand-alone microcontroller-based devices that speak I2C on the MIThril body bus, or analog/digital sensor daughter boards for the SAK2 sensor hub. Currently available stand-alone sensor designs include accelerometers, IR active tag readers, battery monitors, and GPS units. Any number of these sensors can be combined through the use of the MIThril body bus and passive junctions.
One major types of SAK2 daughter boards is currently in use: a multi-sensor physiologic board combining a digital tri-axial accelerometer, 1-channel EKG/EMG, 1-channel galvanic skin response (GSR), and skin temperature sensors, analog sensor buffers, and an I2C to serial converter (to attach third-party serial sensors).
The analog ports of the SAK2 also allow us to interface with a wide range of commercially available sensors, including pulse oximetry, respiration, blood pressure, EEG, blood sugar, humidity, and CO2 sensors.